1. Field of Invention
The present invention concerns a light-source device used in liquid crystal projection equipment, more specifically, a light-source device using a short-arc type of high pressure mercury discharge lamp having 0.16 mg/mm3 or more of mercury sealed within a discharge envelope.
2. Description of Related Art
Light source devices having a short-arc type of high pressure lamp attached to a concave reflection mirror made of borosilicate glass are commonly used in liquid crystal projection equipment. Furthermore, various components in addition to the light-source device, especially a plurality of plastic components, are incorporated in liquid crystal projection equipment, but these components are incorporated at high density because of the need for miniaturization.
Incidentally, metal halide lamps having good color rendering in which are sealed mercury and metal halides have been used as conventional light source lamps because the uniform projection on a screen of images having adequate color rendering is required of liquid crystal projection equipment. The demand has risen recently for light sources having an extremely short separation between electrodes as miniaturization and spot light source development have proceeded further. However, in metal halide lamps in which metals having lower excitation energy than mercury are sealed, limits to discharge concentration develop when electrode separation falls below a given level and accommodation of smaller spot light source development becomes difficult.
For that reason, the short-arc type of high pressure mercury discharge lamp in which the mercury vapor pressure during lighting is high, for example, 20 MPa or above, has attracted attention. More than 0.16 mg/mm3 of mercury is sealed in a discharge envelope to raise the mercury vapor pressure to such high levels during lighting, and such short-arc type of high pressure mercury discharge lamps inhibit arc expansion, enhance photo output and improve the color rendering.
The gazettes of Japanese Kokai Publication Hei-2-148561 (U.S. Pat. No. 5,109,181) and Japanese Kokai Publication Hei-6-52830 (U.S. Pat. No. 5,497,049) present such short-arc type of high pressure mercury discharge lamps.
However, discharge lamps that light at such extremely high mercury vapor pressure may suffer damage to their discharge envelope during lighting, and could rupture in extreme cases. If a lamp should rupture, the concave reflection mirror made of glass could also be destroyed by the impact, with the result being that fragments of the concave reflection mirror could fall and scatter. Furthermore, the front aperture of the concave reflection mirror have been covered by an optically permeable glass plate to prevent the scattering of fragments from a broken lamp, but there are cases in which this optically permeable glass plate is also destroyed by the impact of lamp rupture. Of course, other components incorporated densely in the device would be adversely affected if the concave reflection mirror and the optically permeable glass plate covering the aperture at the front of the concave reflection mirror should rupture and fragments should scatter.
Thus, the purpose of the present invention is to provide an optical device in which the concave reflection mirror surrounding a discharge lamp and fragments of optically permeable glass plate covering the aperture at the front of the concave reflection mirror do not fall and scatter even if a short-arc type of high pressure mercury discharge lamp should be ruptured during lighting at extremely high mercury vapor pressure.
To attain such objectives, the invention provides an optical device comprising a quartz glass discharge envelope in which 0.16 mg/mm3 or more of mercury is sealed, a short-arc type of high pressure mercury discharge lamp having sealing sections formed at both ends of said discharge envelope, and a glass concave reflection mirror surrounding the high pressure mercury discharge lamp in which a sealing section of the high pressure mercury discharge lamp is attached, and wherein a scatter prevention film of a polymer material is applied to the outer surface of the concave reflection mirror. By using such a scatter prevention film of polymer material, the extent of damage occurring due to breakage of the concave reflection mirror can be inhibited and the falling of fragments of the concave reflection mirror can be prevented even if the discharge lamp should rupture.
Scatter prevention film made of polymer material is expensive and reducing the area of the scatter prevention film would be desirable. The results of serious examination revealed that the site where cracking of a concave reflection mirror commences lies in a restricted region when a discharge lamp ruptures. Thus, the present invention also concerns an optical device in which said scatter prevention film is applied to the outer surface of the concave reflection mirror in a region of incidence of light over a range within xc2x140xc2x0 of a direction orthogonal to the axis of said high pressure mercury discharge lamp from all of the light radiated from the arc luminance point of the high pressure mercury discharge lamp.
Furthermore, the polymer material of which the scatter prevention film is formed is preferably a fluorine-based resin.
Next, when the aperture at the front of the concave reflection mirror is covered by an optically permeable glass plate to prevent scattering of fragments of a ruptured lamp from the aperture at the front of the concave reflection mirror according to the present invention or when a scatter prevention film is applied to the periphery of an optically permeable glass plate according to the present invention, the falling of fragments of the optically permeable glass plate can be prevented without significantly attenuating the luminous flux.
A mode of implementing the present invention is explained in detail below with reference to the accompanying drawings.